In an Institute of Electrical and Electronics Engineers (IEEE) 802.16m communication system, a typical example of mobile communication systems, sounding channel signals are used to efficiently use a BeamForming (BF) scheme and a Multi User Multiple Input Multiple Output (MU-MIMO) scheme in a Downlink (DL). A sounding channel is an Uplink (UL) channel, and a sounding channel signal is transmitted via each of a number of transmit antennas used by an Advanced Mobile Station (AMS). An Advanced Base Station (ABS) may estimate a DL channel state for the AMS based on the sounding channel signal transmitted via each of the transmit antennas of the AMS. If the AMS, which has the same number of transmit antennas and receive antennas (i.e., has N transmit antennas and N receive antennas), transmits a sounding channel signal via each of the N transmit antennas, the ABS receives the sounding channel signal transmitted via each of the N transmit antennas, and may estimate a DL channel state for the AMS, assuming that a UL channel state for each of the N transmit antennas is equal to a DL channel state for each of the N receive antennas.
However, there might be an AMS whose transmit antennas are less than receive antennas in number. In this situation, the ABS may not accurately estimate a DL channel state based on the sounding channel signals that the AMS transmits via the transmit antennas, making it difficult or impossible to efficiently use the BF scheme and the MU-MIMO scheme for the AMS. This configuration in which the number of transmit antennas is less than the number of receive antennas will be referred to as an ‘asymmetric antenna configuration’, and an AMS having an asymmetric antenna configuration will be referred to herein as an asymmetric antenna configuration AMS, for convenience of description. Therefore, in the IEEE 802.16m communication system, a sounding antenna switching scheme has been proposed for the asymmetric antenna configuration AMSs. The sounding antenna switching scheme will be described below.
In the sounding antenna switching scheme, even an asymmetric antenna configuration AMS may transmit the same number of sounding channel signals as the number of receive antennas by switching antennas because actually, the number of physical antennas may be equal to or greater than the number of receive antennas.
At present, however, it is merely provided that in the IEEE 802.16m communication system, sounding channel signals may be transmitted using the sounding antenna switching scheme as described above, and any specific operation plan for the sounding antenna switching scheme has not been suggested yet.